"Michael Strogoff was not, had never been, blind. A purely human phenomenon, at the same time moral and physical, had neutralised the action of the incandescent blade which Feofar's executioner had passed before his eyes.

It may be remembered, that at the moment of the execution, Marfa Strogoff was present, stretching out her hands towards her son. Michael gazed at her as a son would gaze at his mother, when it is for the last time. The tears, which his pride in vain endeavoured to subdue, welling up from his heart, gathered under his eyelids, and volatilizing on the cornea, had saved his sight. The vapour formed by his tears interposing between the glowing sabre and his eyeballs, had been sufficient to annihilate the action of the heat. A similar effect is produced, when a workman smelter, after dipping his hand in vapour, can with impunity hold it over a stream of melted iron".

The ad shown is for the American version, which used footage from the earlier German version. I've only seen the RKO version and it is very good, with acting kudos going to Anton Walbrook, Fay Bainter and Akim Tamiroff. I think adding Ed Brophy to the mix was a mistake.